Horn aerials



Oct. 13, 1970 w. F. BROWN 3,534,377

HORN AERIALS Filed Jan. 26, 1967 TRANSMITTER! RECEIVER m lZventor torneys awakrww United States Patent Oflice 3,534,377 Patented Oct. 13, 1970 U.S. Cl. 343786 7 Claims ABSTRACT OF THE DISCLOSURE A horn aerial in the form of a metallic cone having an oval cross-section which is symmetrical about its major and minor axes. The aerial also comprises a means for launching plane polarised electromagnetic waves into, or receiving plane polarised electromagnetic waves from, the cone. Preferably the waveguide is so oriented that the E vector of the waves is at 45 degrees to the axes of the cone or is parallel to the major axis of the cone.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to horn aerials.

When the horn aerials of conventional shape are energised in a conventional manner, the resulting radiation pattern tends to have a beam width which is different for different planes of measurement. Also, the resulting radiation pattern has many side lobes and is sensitive to changes in frequency.

Description of the prior art United States patent specification No. 3,173,146 describes aerial horns of rectangular cross-section and having metallic fillets at their corners for narrowing the radiation pattern in the E-plane of the aerials. The optimum cross-sectional area for these corner fillets is found experimentally and empirically. This operation can be both time-consuming and costly.

It is an object of the present invention to provide a horn aerial which may be more easily constructed so that its radiation patterns are nearly the same when measured in two planes at right angles to one another.

It is a further object of the present invention to provide a horn aerial which may be constructed so that its radiation pattern has only a small number of significant side lobes.

It is a still further object of the present invention to provide a horn aerial which may be constructed so that its radiation pattern is relatively substantially independent of the frequency of excitation.

SUMMARY OF THE INVENTION According to the present invention, there is provided a horn aerial in the form of a cone having an oval crosssection, the oval cross-section being symmetrical about its major and minor axes, and including means for feeding plane polarised electromagnetic waves to, or for receiving plane polarised electramagnetic waves from, the cone. The E vector of the electromagnetic radiation may be at substantially forty-five degrees to the axes of the oval crosssection. Alternatively, the E vector of the electromagnetic radiation may lie substantially along the major axis of the oval cross-section. The cone may have an elliptical cross-section and the feeding means may be a rectangular waveguide. It will, of course, be realised that in accordance with the reciprocity theorem the above-defined horn aerial and its feeding means may equally well be used for the transmission and for the reception of electromagnetic radiation.

In order that the invention may be more clearly understood, embodiments thereof will now be described with reference to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation view of a horn aerial,

FIG. 2 is a perspective view of the horn aerial shown in FIG. 1, and

FIG. 3 is an elevation view of a modified form of horn aerial.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 show a horn aerial including a metallic cone 1 of elliptical cross-section which is open at the mouth 6 of the cone. The major and minor axes of the cone 1 are indicated at 2 and 3 respectively. At the apex of the cone 1, there is a rectangular waveguide 4 coupled to the cone 1 through a coupling member 5, so that plane polarised electromagnetic radiations may be launched into the cone 1. The end of the Waveguide 4 remote from the cone 1 is coupled to a transmitter/receiver 7. The sides of the rectangular waveguide 4 are at forty-five degrees to the major and minor axes of the cone. It follows that the E vector (shown in FIG. 1 of any plane polarised electromagnetic radiation launched into the cone 1 by the waveguide 4 will be at forty-five degrees to the major and minor axes of the cone. It has been found that the abovedescribed horn aerial has radiation patterns in planes parallel to the major and minor axes of the cone, and including the longitudinal axis of the cone, which are nearly the same and are relatively substantially independent of charges of frequency of excitation. Also the number of significant side lobes of the radiation patterns is small.

In a modification of the horn aerial shown in FIGS. 1 and 2, the longer sides of the waveguide 4 are arranged to be parallel to the minor axis 3 as shown in FIG. 3. It follows that the E vector of any plane polarised electromagnetic radiation launched into the cone 1 by the waveguide will be parallel to the major axis of the cone. It has been found that with this orientation of the waveguide 4 the side lobes of the resulting radiation patterns are even further reduced.

It has been found that in the embodiment described with reference to FIGS. 1 to 3, small charges in the aspect ratio (that is to say, the ratio of the major axis 2 to the minor axis 3) of the aerial may be used to change side lobe levels. For example, it has been found that when the aspect ratio is approximately 3:1, small changes therein have only a secondary effect on beam width but may usefully be made to minimise side lobe levels or to minimise changes in beam width with frequency. In one case involving the embodiment hereinbefore described with reference to FIG. 3, the aspect ratio was increased to 5:1. This resulted in a substantial reduction in side lobe levels but greater changes in beam width with frequency were experienced.

Provided with material of which the horn is made is suitable, for example, well-tempered copper, the construction of the horn aerial lends itself to controlled deformation. That is to say, the aspect ratio can be readily adjusted. This deformation is preferably done with the aid of templates. The conical form of horn, therefore, makes it possible economically to achieve a required performance.

Although in the above-described embodiment and the modification thereof, the means for feeding electromagnetic waves to the metallic cone 1 is a rectangular waveguide, clearly and other means of launching plane polarised electromagnetic radiation into the cone 1 may be employed.

As hereinbefore intimated, although the above-described embodiments are described and the invention claimed in the following claims are claimed, as if the horn aerial were used in the transmitting mode, it is clear, by the reciprocity theorem, that they will act equally well and with the same advantages in a receiving mode.

Although the horn aerial is hereinbefore stated to be elliptical in cross-section, this cross-section need not be a perfect ellipse. The cross-section of the horn aerial may be of any oval shape which is symmetrical about two axes at right angles, herein termed the major and minor axes.

I claim:

1. A horn aerial comprising:

a metallic conical horn having an oval cross-section,

said oval cross-section being symmetrical about its major and minor axes, and

feeding means placed at the apex of said conical horn and oriented relative to said axes to launch electromagnetic waves into the cone with their electric field vector oriented at substantially 45 to said axes.

2. A horn aerial as claimed in claim 1 wherein said feeding means is a rectangular waveguide havings its sides at substantially 45 degrees to said axes.

3. A horn aerial as claimed in claim 2 wherein the aspect ratio of said cone is 3:1.

4. A horn aerial as claimed in claim 1 wherein said horn is made of a controllable deformable metal so that the aspect ratio of its cross section may be empirically adjusted by a controlled deformation.

5. A horn aerial comprising a metallic conical horn having an oval cross-section, said oval cross-section being substantially symmetrical about its major and minor axes, a rectangular wave guide disposed with its sides at substantially a 45 angle with respect to the axes of said cross-section and receiving means for receiving plane polarized electromagnetic waves from said cone through said rectangular wave guide.

6. A horn aerial as claimed in claim 5 and wherein said horn is made of a controllable deformable metal so that the aspect ratio of its cross-section may be empirically adjusted by a controlled deformation.

7. A horn aerial as claimed in claim 5 wherein the said cone is made of tempered copper.

References Cited UNITED STATES PATENTS 2,851,686 9/1958 Hagaman 343786 2,933,731 4/1960 Foster et a1. 343-786 2,206,923 7/ 1940 Southworth 343-783 2,607,849 8/ 1952 Purcell et al. 343-781 2,907,034 9/ 1959 Brown 343-78l ELI LIEBERMAN, Primary Examiner 

